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Static Issues
The easiest way to get access to something, is to make
is static. This way, you can to it from everywhere in the application, without
having to instansiate it every place you need it.
Consider this piece of code, which saves an order to
the database:
using(IDbCommand command
= DataBase.Connection.CreateCommand())
{
command.CommandText = "INSERT
INTO Customers VALUES('New','Customer'";
command.ExecuteNonQuery();
}
Here is how we define the DataBase class:
public class DataBase
{
static
IDbConection connection;
public static IDbConnection Connection
{
get
{
if
( connection == null)
{
connection =
CreateAndOpenConnection();
}
return
connection;
}
}
}
Even ignoring the pitfall of leaving connections open
for a long time, can you see the problem?
What happen if we are using this on the web, and two
users are trying to view a page at the same time? One of them is likely to get
the "data reader is already open" error. The same issue appear if you
want to work multi threaded.
This is a major issue when using static, and it is
usually the reason for ruling them out. By the way, I'm using static as the
word here, but everything I say here can be said about Singleton as well.
I'll post later how to handle this issue safely on
multi threaded (and web) scenarios while maintianing the ease of use that
static gives us.
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